POCSAG Transmitter for CC1101

A RadioLib-based POCSAG transmitter implementation for the CC1101 radio module with configurable frequency offset capability.

Author: Anders Isaksson (SA7BNB)

Hardware Design: Anders Isaksson

Software Development: Anders Isaksson (based on RadioLib)

Overview

This project enables transmission of POCSAG (Post Office Code Standardisation Advisory Group) pager messages using a CC1101 radio transceiver module connected to a Wemos D1 Mini Pro. The implementation includes a frequency offset feature for precise frequency calibration.

Hardware Requirements

Wemos D1 Mini Pro (or compatible ESP8266 board)

CC1101 transceiver module

LED (optional, for transmission indicator)

Wiring Configuration

CC1101 PinWemos D1 Mini Pro PinCSGPIO 15GDO0GPIO 4GDO2GPIO 2RSTNot connectedSCKGPIO 14 (automatic)MISOGPIO 12 (automatic)MOSIGPIO 13 (automatic)VCC3.3VGNDGND

LED: Connect to GPIO 5 (optional)

Features

Interactive Serial Interface: Send messages via serial monitor with real-time input

Flexible Message Format: Support for both default and custom RIC (Radio Identity Code) addressing

Frequency Offset Calibration: Adjustable frequency offset for precise tuning

Maximum Power Output: Configured for +10 dBm output power

Visual Feedback: LED indicator for successful transmissions

Input Validation: Built-in checks for RIC and message validity

Software Requirements

Arduino IDE or PlatformIO

RadioLib library

Installation

Install the RadioLib library in your Arduino IDE:

Go to Sketch → Include Library → Manage Libraries

Search for "RadioLib"

Install the latest version

Clone or download this repository

Open the .ino file in Arduino IDE

Configure your board settings:

Board: "LOLIN(WEMOS) D1 mini Pro"

Upload Speed: 921600

CPU Frequency: 80 MHz

Upload to your Wemos D1 Mini Pro

Configuration

Frequency Settings

Adjust these parameters at the top of the code:

float BASE_FREQUENCY = 433.92; // Nominal frequency (MHz)

float FREQUENCY_OFFSET = 0.015; // Offset in MHz (15 kHz)

BASE_FREQUENCY: The nominal operating frequency

FREQUENCY_OFFSET: Fine-tuning offset in MHz

Positive values increase frequency

Negative values decrease frequency

Power Output

The transmitter is configured for maximum power (+10 dBm, approximately 10 mW). Modify the power setting in the code if needed:

radio.setOutputPower(10); // Range: -30 to +10 dBm

Usage

Message Format

The transmitter supports two input formats:

With custom RIC: RIC::Message

Example: 123456::Hello World

RIC must be between 1 and 2,097,151

Without RIC: Message

Example: Test message

Uses default RIC 123456

Sending Messages

Open the Serial Monitor (115200 baud)

Wait for the prompt: Enter command:

Type your message in one of the supported formats

Press Enter to transmit

Watch for transmission confirmation

Message Limitations

Maximum message length: 40 characters

Longer messages are automatically truncated

Only ASCII characters are supported

Example Session

RadioLib POCSAG Transmitter Starting...

Base frequency: 433.92000 MHz

Frequency offset: 0.01500 MHz

Actual transmit frequency: 433.93500 MHz

[CC1101] Initializing ... success!

[Pager] Initializing ... success!

[CC1101] Setting maximum power ... MAX POWER SET!

=== POCSAG Message Sender ===

Format: RIC::Message (e.g., '123456::Hello World')

Or just: Message (uses default RIC 123456)

TX Frequency: 433.93500 MHz

Enter command: 123456::Test message

Sending: 'Test message' to RIC 123456

[Pager] Transmitting ... SUCCESS!

Message sent successfully!

Technical Details

Protocol: POCSAG

Baud Rate: 1200 bps

Modulation: FSK (Frequency Shift Keying)

Encoding: ASCII

Default Frequency: 433.92 MHz (adjustable)

RIC Range: 1 to 2,097,151 (21-bit addressing)

Legal & Safety Notice

⚠️ Important:

Ensure you have the appropriate license to transmit on your chosen frequency

Respect local regulations regarding radio transmissions

Be aware of frequency allocations in your country

This project is intended for educational and amateur radio use only

The author assumes no liability for misuse or regulatory violations

Troubleshooting

No transmission

Check wiring connections

Verify power supply (3.3V for CC1101)

Confirm antenna is connected

Check serial monitor for error codes

Frequency offset issues

Use an SDR or spectrum analyzer to verify actual transmission frequency

Adjust FREQUENCY_OFFSET in small increments (0.001 MHz)

Temperature can affect frequency stability

Message not received

Verify RIC matches receiver configuration

Confirm receiver is tuned to the correct frequency

Check transmission power and antenna placement

License

This project is provided as-is for educational purposes. Please check RadioLib's license for library-specific terms.

Acknowledgments

Hardware design and software implementation by Anders Isaksson (SA7BNB)

Built using the excellent RadioLib by Jan Gromeš

POCSAG protocol implementation by RadioLib contributors

References

POCSAG Protocol Information

CC1101 Datasheet

RadioLib Documentation